Hum elimination system



Jan. 17, 1933. BARONE 1,894,656

HUM ELIMINATION SYSTEM Filed July 25, 1950 5 L I F a w I E W i I 1 -n i PO E P. AMP. I FILTER 4 SUPPLY /6 IP SOURCE. I MOD. I RAMP. FILTER I g 5 :J 7 5 I g [1])? M00. I P. AMP. I FILTER I i H l a /4 HAR. GEN. [j]? MOD. RAMP. FILTER I /Z l 2 SOURCE oF-l ExTRANEous l MODULATIONS.

TUNING SYSTEM INVENTOR Salvatore A. Barons.

ATTORN EY Patented Jan. 17, 1933 UNITED STATES rarsur @FFICE SALVATORE A. BARONE, OF LAKEWOOD, OHEO, ASSIGNOR TO .WIRED RADIO,

1N0, OF

NEW YORK, N. Y., A CORPORATION OF DELAWARE HUM ELIMINATICH SYSTEM Application filed July 25,

My invention pertains in general to wired radio transmitting systems and particularly to wired transmitting systems in which means are provided to eliminate undesirable electrical effects.

In the system of wired radio broadcasting in which carrier frequency signal currents are impressed on light and power lines, it has been found that certain elements in the light and power network, such as transformer equipment, sometimes produce an undesirable hum modulation of the carrier frequency currents.

One of the objects of my invention consists in providing an effective system for the elimination of extraneous electrical effects in a wired radio broadcasting system.

Another object consists in providing a method of hum elimination which comprises, transmitting principal and auxiliary carrier currents through a common hum modulation medium, independently receiving these currents, and combining the resultant hum currents in phase opposition.

I accomplish the above desirable objects in a novel hum elimination system, one embodiment of which I have diagrammatically represented in the drawing illustrating my invention diagrammatically as applied to a system of wired radio transmission, which accompanies and forms a part of this specification.

Referring to the drawing in detail, the power supply source 1 is provided in a central station 2. This power supply source 1 serves as a source of commercial light and power current and may be a generator system or transformer equipment. Power lines 3 extend from the supply source 1 and comprise normal distributing means for the commercial electric light and power current. lhe central station 2 and the power supply source 1 in conjunction with the lines 3 are representative of a normal light and power distribution system. It will, of course, be understood that in actual practice the lines 3 would comprise the usual distribution network including suitable transformers. Such distribution transformers, as well as the distribution lines themselves, and also atmos- 1950. Serial No. 470,649.

pheric conditions, produce e2: raneous electrical effects in carrier currents impressed on the distribution network. For simplicity of representation all of these factors which tend to create disturbing electrical effects will be represented in this specification as a source of extraneous modulations.

In accordance with the usual arrangement of a wired radio broadcasting system, a master oscillator 5, or other source of oscillations, and a harmonic generator 6 are provided within the central station 2. The harmonic generator 6 develops a plurality of different carrier frequencies which are fed to the modulatorslO, 11 and 12, respectively. Modulators 10, 11, and 12 are connected to the power amplifiers 7 8, and 9 respectively. The outputs of these amplifiers are directed through filters 13, 14, and 15 and thence through capacitative couplings to power lines 3. In accordance with my invention an auxiliary frequency, different from those supplied to the amplifiers 7 8, and 9 through the modulators 10, 11, and 12, respectively is fed to another power amplifier 16. The output of the amplifier 16 is fed through a filter 17 and thence to capacitative couplings through the lines 3. It will be noted that this carrier frequency is not modulated as are the other carrier frequencies. The filters 13, 14, 15, and 17 are of the band-pass type adapted to restrict the output frequency to definite frequency band. All of the frequencies originating in the central station 2 are subjected to the same extraneous modulations inasmuch as all of the frequencies are impressed upon the same conducting lines 3.

A tuning system 18 is connected to the lines 3 and can be selectively tuned to resonance with any of the frequencies of the filters 13, 14, and 15. A thermionic detector 19 and thermionic amplifier 20 are connected to the output of the tuning system 18 as shown. The output of the tube 19 being connected to the grid of the tube 20 by the transformer 21.

A tuning circuit comprising inductance 22 and capacitance 23 is inductively coupled to an input circuit 24. capacitively coupled to the lines 3. The circuit 2223 is tuned in ressystem of wired radio broadcasting.

onance with the carrier frequency from filter 17 and amplifier 16. This tuned circuitis connected as shown to a detector tube 24 and thence to the primary of a transformer 2". The secondary of the transformer 25 is connected in phase opposition to the secondary of the transformer 21.

The normal wired radio broadcas pro grams comprising the three different frequencies directed through the filters 13, 14, and 15 can be selectively received by the tuning system 18, indicated by the detector 19, amplified at audio frequencies by the amplifier tube 20, and directed through the output transformer 26 to a suitable indicating device.

Under certain atmospheric conditions or under certain conditions sometimes present in power and light distribution networks, the carrier frequencies comprising these three frequency channels will be additionally modulated to produce undesirable noises and electrical effects. Since all of the frequencies impressed upon the lines 3 pass thrraigh the same source of extraneous modulations, it is evident that the auxiliary carrier frequency from filter 17 will be likewise modulated. This auxiliary carrier frequency is detected by the tube 24 and the detected modulating currents comprising the undesirable noises and electrical effects are delivered to the primary of the transformer The secondary of the transformer 25 delivers these extraneous modulating currents to the secondary of I the transformer 21 in phase opposition. The

undesirable and extraneous modulations in the selected frequency received by the tuning system 18 will thus be cancelled out by the same undesirable and extraneous modulations in the auxiliary frequency received by the tuned circuit 22-23.

Such a system provides a convenient and simple method for eliminating hum and extraneous noises which sometimes occur in a 4 Although I have shown a preferred embodiment of my system, it is to be understood that many changes and modifications can be made without departing from the intended scope of my invention. I do not, therefore, desire to limit myself to the foregoing except insofar as may be pointed out in the appended claims.

What I claim as new and original and desire to secure by Letters Patent of the United States is:

1. A hum elimination system comprising means for generating a master carrier current, means for deriving from said master carrier current a plurality of carrier currents of different frequencies, means for 1nodulating only certain of said derived carrier currents with signal frequencies, a receiving system adapted to receive any one of said modulated carrier currents, a receiving system for receiving an unmodulated one of said carrier currents, and means for combining the outputs of said first mentioned receiving system and said second mentioned receiving system, whereby any one of said modulated carrier currents may be combined in phase opposition with said unmodulated one of said carrier currents.

2. A hum elimination system comprising means for generating a master carrier cur rent, means for deriving from said master carrier current a plurality of carrier cur rents of different frequencies, means for mod ulating only certain of said derived carrier currents with signal frequencies, a receiving system adapted to receive any one of said modulated carrier currents, a receiving system for receiving an unmodulated one of said carrier currents, wire lines connecting said source of carrier currents and said receiving systems, and means for combining the outputs of said first mentioned receiving system and said second mentioned receiving system whereby any one of said modulated carrier currents may be combined in phase opposition with said umnodulated one of said carrier currents.

SALVATORE A. BARONE. 

